At 05:10 AM 18/06/2011, you wrote:
>I am looking for a pot and not having much luck so I thought I'd ask
>here. My controller uses a 5K pot, Max speed is at 5K ohms, I think
>this is the reverse of normal setups. I would like to have a center
>"off" pot to make a forward reverse throttle lever. I can use cams
>and micro switches for the for/rev solenoids.
>But I cannot come up with a simple easy setup for the pot.
>Any suggestions?
G'day ...um Matt?
I had to convert a joystick-operated forklift to a Curtis controller,
that had the same 0 to 5k 0 to full speed requirement. What I did was
as follows:
The original joystick included a pair of gears to 'speed up' the pot
motion, so it actually turned the pot about half of the normal
240-degree rotation each way, so I had to use a 10K pot. The type I
used was a ceramic-substrate (cermet) with no mechanical stop
[similar to
http://au.element14.com/vishay-spectrol/357b0103mab251s22/potentiometer-1w-10k/dp/1144764
. Ebay worldwide gets 8000+ hits for "potentiometer", asking for
'"stopless potentiometer" gets zero hits, so may need to go to an
electronic supply house such as mouser, Newark, etc. to get what you need].
I marked the original 'end' (open circuit) zone relative to the
shaft, then prised out the back, and cut the track at a point
opposite the end dead zone (just roughed at it with a 'dremel'
grinder until I could measure the disconnect between the halves, then
gave it a little more for good measure). Epoxy glue put the pot back together.
I turned the pot to its' original end zone (would not want to be
running back and forwards across the ground out part) and mounted it
into the joystick. Connecting the two ends together makes the wiper
contact one or other end, then as it continues to turn away, the
resistance increases up to just under 5k before it hit the ground out
part (curtis controllers hit 100% at about 4.8k usually, so not a problem).
If you only need a small amount of rotation, the pot value could be
in the order of 100k-ohms, giving about 17 degrees each side of
center, with no need to break it open and cut the track, since the
remaining path to the 'other' end is insignificant. A 50k 'pot' would
give around 35 degrees each side of center, although probably need to
be a little more than that due to the parallel path around the
'unused' side of the pot.
Although these types of potentiometers are not cheap (in the
industrial world they are considered relatively low cost, similar
ones can easily run over $100 just for a pot), they are well made, of
corrosion-resistant materials and come with a manufacturers' spec of
5 million rotations.
And if you are wanting to put the pot straight into the end of your
operating lever, a 50k-ohm one turning 35 to 40 degrees each side of
center means no modifications to the 'pot', microswitches or
forward/reverse and fulfills the requested "simple easy setup for the pot".
Hope this helps
Regards
[Technik] James
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